Understanding the Impacts of Hydroelectric Power, Mining, and Other Land Use Activities that Alter Water Temperatures and the Resulting Thermal Effects on Coldwater Fishes Such as Salmon and Trout

TASA ID: 537

Streamflow alterations associated with hydroelectric power, water diversions, mining, and other land use activities can alter water temperatures in rivers and streams.  Water diversions associated with hydroelectric plants can impact stream flows that, in turn, may increase water temperatures (PG&E, 2006; Rich, 2007). Diversion of water for irrigation and municipal uses often results in increased water temperatures in rivers and streams (Monsen et al., 2007).  Gravel mining may involve extensive riparian clearing and often results in diversion of flow and excavation of deep pits (Bull and Scott 1974; Kondolf 1997).  Loss of streamside cover and dredging of the streambed can increase water temperatures (YCPD and WSDE, 2003).  And, other types of mining may incorporate water diversions that, in turn, can increase water temperatures in coldwater rivers and streams.

Changes in water temperatures can affect coldwater fishes, such as salmon and trout (salmonids) (Rich, 2007, 2000, 1987), either detrimentally or beneficially, depending upon other environmental factors.  Of all the life-stage requirements of temperature-intolerant fishes, such salmonids, water temperature is the most important, yet, commonly, the least understood.  Water temperature can be considered in two ways: (1) Physiologically, such as its role in basic metabolism, development, and growth; or (2) As a factor that can be stressful or even result in the death of a fish.  Depending upon the environmental circumstances, water temperature impacts on salmonids can be either beneficial or detrimental.  However, I have found that the precise understanding of water temperature impacts on salmonids is often hindered by the following:

• Lack of understanding of how fish respond to water temperature changes
• Use of death, rather than sublethal impacts, to determine how fish respond to water temperature changes
• Lack of site-specific studies
Lack of standardization of methodologies used for water temperature studies
• Misinterpretation of the results of water temperature studies.

Fishes are cold-blooded animals (poikilotherms), which means that their internal body temperature varies, according to the external environment.  This is in contrast to us, as mammals, who are warm-bloode(homeotherms).  We, as mammals, maintain our internal body temperature constantly at about 98.6 ^oF, unless we are sick.  Having a constant internal temperature is very important, physiologically; it enables blood to flow, metabolic reactions to proceed, and various other processes to occur, all at a fairly constant rate.  Unless we physically exert ourselves, or are sick, for the most part, all of these physiological actions are constant for any given person.  This ability to control our internal temperature, regardless of what is occurring outside, is called thermoregulation.  By contrast, fish species, such as salmonids, are at the constant mercy of the thermal characteristics of their environment.  As a result of being cold-blooded, a fish will try to compensate for changing water temperatures either through: (1) Physiological changes or (2) Behavioral changes.  

Usually, a fish has little physiological control over its body temperatures; if the water is hot, the fish is hot, and if the water is cold, the fish is cold, etc.  Thus, fish have no physiological way to quickly acclimate to changes in water temperature.  And, a fish's metabolism, which controls all aspects of its body, is directly proportional to water temperature, within given limits.  Thus, as water temperatures increase, so does the fish's metabolic rate and the need for food.  If there is enough food available and dissolved oxygen conditions are sufficient, then the fish will grow, within certain thermal ranges.  But, if the amount of food is limited and/or other stressors (e.g., low dissolved oxygen, pollution, etc.) prevail for any period of time, the fish may die immediately, or at some time in the future.

However, sometimes environmental conditions provide opportunities for salmonids to use behavior to thermoregulate.  This of great importance when their habitat provides more than one thermal option.  For example, in studies on the Navarro River in Mendocino County, California, juvenile coho salmon were collected at water temperatures that would be considered stressful, according to results from other studies reported in the scientific literature (Rich, 1991).  However, the young coho salmon in the Navarro River had good growth rates and appeared to be healthy.  It was concluded that both the abundant food resources and presence of cool thermal "refugia" accounted for their ability to thrive in what was reported elsewhere to be stressful water temperatures.  Thus, with the thermocline (i.e., the different water temperatures in the pool, depending upon the pool depth) in the pools, the cooler areas provided a refuge for the salmon during the hot part of the day.  The fish could then digest their food at physiologically acceptable (i.e., cooler) water temperatures, even though a large percentage of their pool habitat was characterized by high water temperatures.

Although a water temperature study, whose endpoint is death, is easy to undertake and has a specific outcome (i.e., death), sublethal stressful water temperatures, while not always immediately resulting in the death of a salmonid, often result in a reduction in the population over time (Brett, 1956).   Less than optimal water temperatures become a problem when they impair the fish in some way, such as resulting in a significant disturbance to the normal functions of the fish, and, thus, decreasing the probability for the fish's survival.  Established indicators of thermal stress on fish include: (1) Disease outbreaks; (2) Reduction in growth; (3) Reduction in food conversion efficiency; (4) Loss of appetite; (5) Hyperactivity; and, (6) Secretion of stress hormones such as adrenalin (Elliott, 1981).  All of these stress indicators have been directly and indirectly linked to the survival of natural populations of salmonids and other fish species.  In addition, the stressful impacts of water temperatures on salmonids are positively related to the duration and severity of the exposure. Thus, the longer the salmon or trout is exposed to thermal stress, the less chance it has for long-term survival.

One should be very cautious drawing conclusions about how salmonids may respond to water temperatures in the "natural world," based on how they respond under controlled laboratory or hatchery conditions.  Most physiological and other thermal studies have been conducted under laboratory conditions, where one is able to control the environment, unlike in a river or stream.  In the controlled environment of a laboratory or a hatchery, where fish do not have to escape predators or search for food, no energy is spent on these day-to-day energy draining tasks.  Furthermore, many of the factors known to affect the outcome of thermal experiments have not been consistently documented.  In addition, different geographical areas have different conditions.  Hence, one should not assume that the results from a laboratory study or a study conducted in one geographical area will be the same as those for a creek or river system in another geographical area.  Finally, the cumulative effects of stress that fish experience in the wild compound the problems of applying water temperature data collected in the laboratory with those collected in field situations. When a salmonid is under stress in the natural world, adding the stress of high water temperatures for any period of time compounds the problem and, ultimately, reduces the chance of survival and/or being able to successfully reproduce.  Thus, to determine the effects of water temperatures on any fish species, including salmonids, site-specific thermal studies are essential.

The variety of methodologies used to assess thermal impacts can result in a variety of interpretations of the data.  The lack of standardized methodologies has resulted in a variety of definitions for the same term.  Similar to all specific areas of scientific inquiry, the terminology used to define impacts of water temperature on fishes has its own nomenclature which can be confusing when there are different meanings for terms such as, "optimal," "lethal," "preferred," "tolerance," "threshold," and "stressful" temperatures.  Such a lack of standardization is problematical, when one compares the results of one "optimal temperature" study with that of another, and the results of the former study are based on "thermal tolerance" while those of the latter are based on a "growth rate."  Similarly, the term "lethal" can be used literally, as a percentage of the eggs or fish that die.  But the term "lethal" is often also used by fish physiologists to identify the temperature at which 50% of the eggs or fish die within 28 days, or seven days, or 14 hours (Fry et al., 1942) or 12 hours (Brett, 1944), when previously acclimated to the highest possible temperature that will not result in death.  Thus, when interpreting thermal data, it is extremely important that one knows the definitions of the thermal terms used in the experimental protocol.

Another problem with determining the water temperature impacts of salmonids from land uses is one of misinterpretation of the results of prior studies.  The general concept of fish bioenergetics is not difficult to comprehend.  Bioenergetics has to do with how organisms, including humans, use their food.  The food eaten can be used for metabolism, growth, swimming away from predators.  However, the results from salmonid bioenergetics studies are often misinterpreted and misapplied; it is often difficult for the non-fish physiologist to understand the results of such studies.  Thus, a problem occurs when fisheries biologists use the results of previous studies inappropriately in their quest for "a number," whether it is a number for an "optimal temperature," a "stressful temperature," or a "lethal temperature" for coldwater fish, such as a salmon or trout. Without an accurate interpretation of the results of a study, it is not possible to determine the impacts of water temperatures on salmonids.

Following are three examples of such misinterpretations/misapplications that I have observed.

• "Inputting" field data directly into an unvalidated model. Unless site-specific studies are undertaken, one has no idea whether or not the model is valid. An example of this can be found with the agency use (e.g., National Marine Fisheries Service, U.S. Forest Service) of what is called the Maximum Weekly Average Temperature (MWAT)Method. In an attempt to advance beyond the search for a "magic number" in establishing theoretical temperature tolerance limits for fishes, the MWAT model was originally designed in 1977 (Brungs and Jones, 1977). However, the MWAT Model, or hypothesis, was never validated in the field. In recent years, there has been an increasing number of examples from field studies that have invalidated the MWAT Model.  For example, the MWAT Model results in optimal and lethal thermal ranges of 5-17 C and 23-25 ºC, respectively, for juvenile coho salmon.  However, after the 1980 Mt. St. Helens eruption in Washington state, juvenile coho salmon were collected in streams where water temperatures exceeded 20 ºC during much of the summer months.  Despite a thermal environment that the MWAT Model calculated to be thermally stressful for the juvenile coho salmon, both growth and survival rates were higher during these months than during those times when water temperatures were considered non-stressful (i.e., below 15.6 º C), accordingly.  And, the long-term (i.e., 3-6 years post-eruption) consequences of the elevated water temperatures demonstrated a high population of coho salmon (Bisson et al, 1985). Thus, to determine impacts of land uses, it is extremely important to use site-specific information.


• Transferring numbers (e.g., percent mortality, thermal optimal) from a laboratory study to a field situation in another geographical area. The impacts of water temperature are not only species- and life stage-specific, they are site-specific, as well.  In addition, in the wild, fish do not feed maximally, because the energy needed to capture food exceeds the growth benefits. Thus, the results of laboratory studies in which salmonids are fed maximal food rations are never equivalent to what the salmonids experience in the natural environment.


• As support for a previously-determined "endpoint," sometimes fisheries biologists select only some of the scientific studies reported in the scientific literature on the subject. This is an unfortunate problem because, by selectively excluding some of the studies, one does not have an accurate representation of the range of thermal impacts that have been reported in the scientific literature.  The range of results reported in the scientific literature may be due to different study methodologies, different definitions for the same term, different sizes of salmonids, or other factors that are not comparable from study to study.  Thus, one cannot accurately establish non-  stressful thermal ranges for a given life stage of a given species.  And, without the ability to establish thermal requirements, it is not possible to determine the impacts of water temperature from land uses on salmonids.

In summary, to determine the water temperature impacts (either beneficial or adverse) of hydroelectric power, water diversions, mining or other land use activities on coldwater fishes, such as salmon and trout, it is important to: (1) Understand how salmonids respond to water temperature changes; (2) Use site-specific studies; and (3) Know how to interpret the results of water temperature studies on salmonids.

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Brett, J. R.  1956.  Some principles in the thermal requirements of fishes.  Quarterly Review Biology 31: 75-87.

Brett, J. R.  1944.  Some lethal temperature relations of Algonquin Park fishes.  University Toronto Studies Biology Series. 52: 49 pp.

Brungs, W. A. and B. R. Jones. 1977.  Temperature criteria for freshwater fish:  protocol and procedures.  EPA-600/3-77/061.  U.S. Environmental Protection agency, Environmental Research Laboratory, Duluth, Minnesota.

Bull, W. B. and K. M. Scott. 1974.  Impact of mining gravel from urban stream beds in the southwestern United States.  Geology 2:  171-174.

Fry, F. E. J., J. R. Brett and G. H. Clawson.  1942.  Lethal limits of temperature for young goldfish.  Review Canada De Biology. 1: 50-56.

Kondolf, G. M.  1997.  Hungry water:  effects of dams and gravel mining on river channels. Environmental Management 21:  533-551. 

Monsen, N. E., J. E. Cloern, and J. R. Burau. 2007.  Effects of flow diversions on water and habitat quality:  examples from California's highly manipulated Sacramento-San Joaquin Delta.  San Francisco Estuary & Watershed Science. Volume 5, Issue 3 (July 2007). Article 2.

PG&E (Pacific Gas and Electric Company).  2006.  Crane Valley Hydroelectric Project, FERC No. 1354 Crane Valley Water Temperature Monitoring Results - 2005 Addressing License Article 405 and U. S. Forest Service Condition No. 5.  44 pages +Appendices

Rich, A. A. 2007.  PG&E's DeSabla-Centerville Hydropower Project - Comments on the Thermal Effects    of PG&E's DeSabla-Centerville Project on Spring-Run Chinook Salmon (Oncorhynchus tshawytscha).  Written Expert Witness Testimony Submitted into the Administrative Record, oN Behalf of the California Sportfishing Protection Alliance, Berkeley, California.  August 23, 2007. 25 pages plus Appendices.

Rich, A. A.  2000.  Thermal Impacts of the Yuba County Water Agency's Stream Flow Plan on Juvenile      Chinook Salmon and Steelhead.  Oral and Written Expert Testimony Submitted to the California State Water Resources Control Board on Behalf of the California Department of Fish and Game, Regarding the Yuba River Hearings.  May 1, 2000.

Rich, A. A. 1991.  The impacts of timber harvest practices on the fishery resources of the Navarro River Watershed, Mendocino County, California.  Phase III:  Fishery resources baseline surveys. 

Annual Report.  Prepared for Louisiana-Pacific Corporation, Samoa,  California, July 7, 1991. 109 pp.
+ Appendices.

Rich, A. A.  1987.  Water Temperatures which Optimize Growth and Survival of the Anadromous Fishery Resources of the Lower American River.  Oral and Written Expert Testimony Submitted to the California State Water Resources Control Board on Behalf of County of Sacramento and the California Department of Fish and Game.  April, 1987.  24 pp + Appendices.

YCPD and WSDE (Yakima County Planning Department and Washington State Department of Ecology).     2003.  Floodplain mining impact study: thermal investigations-Interim Report.  April 15, 2003. 

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